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Evolution of South Atlantic density and chemical stratification across the last deglaciation

Roberts, Jenny; Gottschalk, Julia; Skinner, Luke C.; Peck, Victoria L.; Kender, Sev; Elderfield, Henry; Waelbroeck, Claire; Vázquez Riveiros, Natalia; Hodell, David A.. 2016 Evolution of South Atlantic density and chemical stratification across the last deglaciation. Proceedings of the National Academy of Sciences, 113 (3). 514-519. https://doi.org/10.1073/pnas.1511252113

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Abstract/Summary

Explanations of the glacial–interglacial variations in atmospheric pCO2 invoke a significant role for the deep ocean in the storage of CO2. Deep-ocean density stratification has been proposed as a mechanism to promote the storage of CO2 in the deep ocean during glacial times. A wealth of proxy data supports the presence of a “chemical divide” between intermediate and deep water in the glacial Atlantic Ocean, which indirectly points to an increase in deep-ocean density stratification. However, direct observational evidence of changes in the primary controls of ocean density stratification, i.e., temperature and salinity, remain scarce. Here, we use Mg/Ca-derived seawater temperature and salinity estimates determined from temperature-corrected δ18O measurements on the benthic foraminifer Uvigerina spp. from deep and intermediate water-depth marine sediment cores to reconstruct the changes in density of sub-Antarctic South Atlantic water masses over the last deglaciation (i.e., 22–2 ka before present). We find that a major breakdown in the physical density stratification significantly lags the breakdown of the deep-intermediate chemical divide, as indicated by the chemical tracers of benthic foraminifer δ13C and foraminifer/coral 14C. Our results indicate that chemical destratification likely resulted in the first rise in atmospheric pCO2, whereas the density destratification of the deep South Atlantic lags the second rise in atmospheric pCO2 during the late deglacial period. Our findings emphasize that the physical and chemical destratification of the ocean are not as tightly coupled as generally assumed.

Item Type: Publication - Article
Digital Object Identifier (DOI): https://doi.org/10.1073/pnas.1511252113
Programmes: BAS Programmes > BAS Programmes 2015 > Palaeo-Environments, Ice Sheets and Climate Change
ISSN: 0027-8424
Additional Keywords: South Atlantic, density gradient, Ocean stratification, last deglaciation, atmospheric CO2
Date made live: 26 Jan 2016 13:32 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/512714

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